The invention discloses a mandrel stripping device as well as a system and a method for determining the viscosity of prepreg in a mandrel stripping way, and belongs to the technical field of materialphysical property testing. The mandrel stripping device comprises a base, a traction mechanism, a sample plate for pasting a prepreg sample, and a stripping mandrel, wherein the stripping mandrel is rotationally arranged on the base; the sample plate is arranged on the base in a sliding way through a guide rail slide block mechanism; the traction mechanism comprises a first pulley which is rotationally arranged on the base, and a traction rope winding across the first pulley; the first pulley is located on one end side of a linear guide rail; one end of the traction rope is fixedly connected with one end of the sample plate; the other end of the traction rope is used for pulling the sample plate to slide in a stripping process, and the sliding speed is equal to the stripping speed of the prepreg sample. The stripping device can be used for quantitatively determining physical quantities representing the viscosity and bending stiffness of the prepreg by combining the device with a universal testing machine.